This invention relates to a working method and an apparatus for applying a liquid medium to a printing carrier in offset printing machines. The apparatus is suitable for processing low-viscosity and higher-viscosity media, such as, for example, dispersion lacquer on an aqueous basis (low-viscosity with a viscosity .ltoreq.0.1 Pa s) or bronze and effect printing ink with a specific pigment proportion (higher-viscosity with a viscosity of 0.1 to 2 Pa s) such as, for example, gold lacquer.
Various arrangements are known for applying liquid media to a printing carrier. According to DE 3,427,898 C1, the metering of the medium to be applied takes place by means of a metering roller and an applicator roller according to the principle of squeeze rollers, the liquid (e.g., lacquer) being supplied to the roller gap by means of a tube so as to form a lacquer wedge.
A chamber-type doctor is known from EP 0,071,180 A1 and is essentially forme by a housing with side walls and doctor blades, also called squeegees, attached to the housing. The doctor blades are supported on the applicator roller, and the liquid is transferred to the screened applicator roller via the chamber thus forme. In this case, the chamber-type doctor is pivotably mounted in a holder arranged above the applicator roller and can be engaged against the applicator roller by an operating cylinder acting on the holder.
The known arrangements are disadvantageous in that they do not guarantee precise metering of the medium to be applied in the case of media of different viscosity. The known arrangements thus cannot be used universally for applying the respectively used liquid to the printing carrier.